package tencent

// 递归的思路:
func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {
	if l1 == nil {
		return l2
	}
	if l2 == nil {
		return l1
	}
	if l1.Val <= l2.Val {
		l1.Next = mergeTwoLists(l1.Next, l2)
		return l1
	}
	l2.Next = mergeTwoLists(l1, l2.Next)
	return l2
}

//迭代的思路
func (Solution1) mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {
	//哨兵
	node := &ListNode{}
	head := node
	for l1 != nil && l2 != nil {
		if l1.Val <= l2.Val {
			node.Next = l1
			l1 = l1.Next
		} else {
			node.Next = l2
			l2 = l2.Next
		}
		node = node.Next
	}
	if l1 == nil {
		node.Next = l2
	} else {
		node.Next = l1
	}
	return head.Next
}
